This proposal is to continue studies to characterize the hr-t gene of polyoma virus and its role in virus growth and malignant cell transformation. We shall seek to characterize the small and middle tumor antigens which constitute the dual products of the hr-t gene. Specific aims include: 1), mapping of sites of in vivo phosphorylation of mT antigens by cellular kinases, and the potential role these phosphorylations have in activating the mT-associated tyrosine-specific kinase activity; 2), use of synthetic peptide antigens to raise antisera capable of reacting specifically with mT protein; 3), use of such antisera to affinity purify mT proteins; 4), determine whether the tyrosine kinase activity is intrinsic to mT or resides in a cellular enzyme; 5), studies of cellular phosphoprotein metabolism and how its affected by hr-t viral gene, using an anti-phosphotyosine antiserum and other approaches; 6), studies on the role of the hr-t gene in virus maturation, possibly at the level of capsid protein phosphorylation; 7) studies directed toward sT antigen, its isolation and purification, and functional properties, and, 8), studies directed toward the 36K and 63K "non-viral" tumor antigens, their associations with viral proteins, and possible functional significance.